PALLADIUM-LANTHANUM CATALYSTS FOR AUTOMOTIVE EMISSION CONTROL.

Recent efforts to provide Rh-free three-way catalysts have resulted in Pd-La//2O//3/ alpha -Al//2O//3 with desirable catalytic activities. The performance of the Pd-La//2O//3 catalyst was examined in engine exhaust gas and simulated exhaust gas. Also, the activities for H//2-NO, H//2-NO-O//2, CO-H//2O, and propylene-H//2O reactions, chemisorption, and TPD were measured. A/F dependence of Pd-La//2O//3 catalyst was almost similar to that of Rh catalyst, and the NO conversion of Pd-La//2O//3 catalyst during warm-up conditions was much better than that of Pd catalyst in engine exhaust control. These data demonstrate that the presence of La//2O//3 on the Pd-La//2O//3 catalyst has three effects. First, it increases the activity and selectivity of Pd catalyst for NO reduction by H//2. Second, it increases the activities for CO and propylene reactions with H//2O. Third, it increases the amount of NO chemisorption. This means that through the three-way catalyst reactions, the role of La//2O//3 is an excellent NO reserver and an abundant H//2 supplier.